Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Dr. Keith Rodewald

Second Advisor

Dr. James Kopp

Third Advisor

Dr. Arthur Snapper


Various models have been used to describe the nature of the relation between reinforcement delay and relative response rate. Delay has been incorporated as one aspect of reinforcement within the matching law which states that the relative response rates in concurrent schedules will equal the relative immediacy of the reinforcement. A variation of matching applicable in concurrent-chain schedules states that the relative rates of responding in the initial links will match the relative reduction in the average delay to reinforcement correlated with the entry to each terminal link. The momentary maximizing position states that the molar matching relation is a product of a more general molecular phenomenon of maximizing. Data have been provided on the sequential patterns of left and right pecks which indicate that in choice situations, responses are emitted to the key which has the greatest momentary probability (or value) of reinforcement. Because of the manner in which concurrent variable-interval schedules assign reinforcement, the probability of reinforcement for a given alternative changes as a function of time and responding. Momentary maximizing in this situation averages over a session to produce the matching relation.

If one assumes maximizing to be the underlying process responsible for behavior in choice situations, then one accepts its basic premise that preference is exclusive for the better alternative at the moment. If one alternative always produces the better outcome, it should always be chosen. A lack of exclusive preference could be attributed to a failure to discriminate between the alternative reinforcers or to some uncontrolled factors producing a bias to the other alternative. The problem then becomes a psychophysical one involving the reinforcer as the stimulus which can be varied along a number of physical dimensions.

The present study was designed to be a psychophysical analysis on the dimension of reinforcement delay to obtain indexes of discriminability in rats. A discrete trial procedure was used where the better outcome (shorter delay) was always available for one alternative. A lamp was illuminated over the lever which produced the shorter delay. Both levers were retracted during the delay and until the start of the next trial. The absolute value of the longer delay was varied across groups of rats (4, 8, and 12 seconds). Within each group the difference between the longer and shorter delay was decreased over conditions by increasing the duration of the shorter delay. After a point of indifference was found, the difference between delays was made progressively larger.

At each difference between delays, a signal detection measure of discriminability was obtained. The signal detection analysis was chosen because of its advantages over conventional psychophysics in factoring out the effects of uncontrolled biasing factors. The signal detection measure of sensitivity was found to decrease as the difference between delays was decreased. When the difference between delays was then increased, the measure of sensitivity remained low for most rats. A comparison of data across groups of rats suggested that the sensitivity measure was a function of the relative rather than the absolute difference between delays.

Access Setting

Dissertation-Open Access